1. Field of the Invention
The present invention relates a high frequency switch, which is to be usable for a radio equipment.
2. Related Art
An example of a conventional microwave switch, which is to be used for a receiving unit of a radio equipment, for example, is illustrated in FIG. 3, and the switch shown in FIG. 3 is a single-input/single-output switch, which will hereinafter be referred to as the “SPST (Single-Pole Single-Throw) switch” utilizing diodes, in which an antenna is commonly utilized for transmitting and receiving units. That is, in the switch of FIG. 3, a diode 31 is arranged between an input terminal 34 and an output terminal 35 and another diode 32 is provided in a terminated line so as to be in parallel to the diode 3s, to which a terminating resistor 33 is connected.
In this arrangement of the switch in FIG. 3, in a case that the diode 32 is made OFF while keeping the diode 31 in an ON position, a high frequency signal, which has been inputted from the input terminal 34, is outputted to the output terminal 35. Such a state will be hereinlater referred to as a “passing state”.
On the other hand, in a case that the diode 31 is kept in an OFF position and the other diode 32 is kept in an ON position, the high frequency signal, which has been inputted from the input terminal 34, passes through the diode 32 and then is absorbed by the terminating resistor 33. Such a state will be hereinlater referred to as an “absorbed state”.
The SPST switch as shown in FIG. 3, which is now kept in the absorbed state, causes the input signal to be absorbed by the terminating resistor, thus providing an appropriate VSWR (voltage standing wave ratio) of the input terminal 34. However, the diode 31 is kept in the OFF state, with the result that the input signal is subjected to an almost total reflection to thereby deteriorate the VSWR of the output terminal 35, thus causing inconvenience and being defective.
Furthermore, there is provided Japanese Laid-Open Patent Application No. H9-181641 (hereinafter referred to as the “Prior Art Document 1”), which describes, especially on page 2 and in FIG. 1, as another example of the conventional high frequency switch, a single-input/multiple-output switch utilizing FETs (field-effect transistors). The disclosed high frequency switch utilizes an inductor for preventing, when a certain FET is kept in an ON position to generate an input signal to an output terminal, occurrence of conductive loss due to capacity of another FET in an OFF position. However, the Prior Art Document 1 fails to teach the prevention of deterioration in the VSWR of the input and output terminals.
As mentioned above, the conventional SPST switch shown in FIG. 3 can provide an appropriate VSWR on the input side with the use of the terminating resistor connected to the side of the input terminal in the absorbed state of the switch circuit. However, the almost total reflection occurs on the output side, which causes the deterioration of the VSWR.